期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1998
卷号：95
期号：25
页码：14622-14627
DOI：10.1073/pnas.95.25.14622
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Recently, cryoelectron microscopy of isolated macromolecular complexes has advanced to resolutions below 10 A, enabling direct visualization of -helical secondary structure. To help correlate such density maps with the amino acid sequences of the component proteins, we advocate peptide-based difference mapping, i.e., insertion of peptides, {approx}10 residues long, at targeted points in the sequence and visualization of these peptides as bulk labels in cryoelectron microscopy-derived difference maps. As proof of principle, we have appended an extraneous octapeptide at the N terminus of hepatitis B virus capsid protein and determined its location on the capsid surface by difference imaging at 11 A resolution. Hepatitis B virus capsids are icosahedral particles, {approx}300 A in diameter, made up of T-shaped dimers (subunit Mr, 16-21 kDa, depending on construct). The stems of the Ts protrude outward as spikes, whereas the crosspieces pack to form the contiguous shell. The two N termini per dimer reside on either side of the spike-stem, at the level at which it enters the shell. This location is consistent with formation of the known intramolecular disulfide bond between the cysteines at positions 61 and -7 (in the residual propeptide) in the "e-antigen" form of the capsid protein and has implications for why this clinically important antigen remains unassembled in vivo.
关键词：hepatitis B virus core antigen/virus capsid structure/three-dimensional image reconstruction
